One known extrusion pulling apparatus incorporates extrusion puller jaws composed of an upper and lower jaw wherein the upper jaw comprises a plurality of multi-toothed fingers and the lower jaw comprises a flat serrated plate. One jaw moves relative to the other to allow for opening and closing movement of the jaws for gripping and releasing of an extruded workpiece. Typically, the upper jaw moves relative to a fixed lower jaw and a sufficient amount of gripping pressure is applied to the workpiece by the jaws so that the extrusion apparatus can pull the workpiece from the die.
FIG. 1 (prior art) and FIG. 1A (prior art) (hereinafter known as the "Smith Design") illustrate a known upper jaw finger 10A and a lower jaw 12A in an extrusion puller apparatus for gripping an extruded workpiece 14A. The upper jaw finger is comprised of a body l6A, means for mounting the finger 18A into the upper jaw and a plurality of gripping teeth 20A. Each of the teeth is comprised of a leading edge 22A and a trailing edge 24A. The angle created between the leading edge 22A of one tooth and the trailing edge 24A of the preceding tooth is the attack angle A.
The upper jaw typically is pivotably mounted relative to the fixed lower jaw 12A. The upper jaw pivots downward until the teeth of both jaws engage the workpiece 14A and applies force thereto to create sufficient gripping pressure on the extruded workpiece 14A. The pivotable movement of the upper jaw causes the teeth 20A to travel along an arc B during the gripping and releasing movement of the jaws. The teeth 20A of the jaw finger 10A may contact the workpiece 14A anywhere along arc B depending on the profile of the workpiece 14A.
Because of the large number of teeth 20A on each upper jaw finger 10A of the Smith Design, the attack angle A on the Smith Design is relatively small. Therefore as the upper jaw finger 10A pivots downward the teeth travel along arc B until a first tooth 23A enters the workpiece 14A. But, before all of the body of the first tooth 23A penetrates the workpiece 14A, the flat trailing edge 24A of the preceding tooth 25A contacts the workpiece 14A. The flat trailing edge 24A of the preceding tooth 25A cannot penetrate the surface of the workpiece 14A without a great amount of pressure from the upper jaw. Without this extremely large force, the gripping strength of the jaws may be inadequate and often results in slippage of the workpiece 14A within the jaws.
The lower jaw 12A of the Smith design comprises a plurality of serrations 26A which extend perpendicular to the extrusion axis and are spaced a short distance apart. The serrations 26A are composed of a plurality of peaks 28A and valleys 30A or may be a saw tooth design (not shown). The Smith design utilizes a plurality of small serrations as shown in FIG. 1 (Prior Art).
The U.S. Pat. No. 4,566,298 to Elhaus (issued Jan. 28, 1986) discloses an extrusion puller incorporating a plurality of clamping segments or puller fingers. This concept is also disclosed in the U.S. Pat. No. 3,188,539 to Harwood et al (issued Jan. 21, 1964), the U.S. Pat. No. 4,307,597 to Elhaus et al (issued Dec. 29, 1981) and the U.S. Pat. No. 3,881,339 to Mannell (issued May 6, 1975).
The Mannell patent also discloses the concept of providing springs or other biasing means to each of the individual fingers to allow for the gripping of a complex-shaped workpiece.
The concept of incorporating a plurality of serrated jaws for gripping a workpiece during extrusion is disclosed in the U.S. Pat. No. 4,522,091 to Toffolon (issued June 11, 1985) and the U.S. Pat. No. 3,078,984 to Baker (issued Feb. 26, 1963).